I just don't relly on the exercise itself to burn fat, the amount of fat you can burn on a cardio session after your glycogen stores are all used up (takes a while for that to happen) is really minimum compared to how much fat you can burn throughout the day by chosing exercises that will build muscle and raise your metabolism (One lb of fat can supply you with enough energy to perform about 10 hours of
medium intensity cardio). You can greatly minimise your efforts (training volume) and maximize results if you choose the proper exercises, technics and nutrition.
Short cardio sessions (around 20mins) of
high intensity interval cardio (1min sprint, 2mins slow jog) work really good to produce GH wich will burn fat throughout the day, lifting in the 10 reps range with short rest between sets will do the same (if your goal is fat burn only), I recommend working in the 4-6 reps range though because it not only raises GH levels but it also raises Test levels a lot.
You got to make your hormones do the job for you...